The present invention relates to pattern forming methods for use in, for example, processes for fabricating semiconductor devices
With increasing integration of semiconductor integrated circuits and downsizing of semiconductor elements, there has been a demand for acceleration of the development of lithography techniques. At present, pattern formation is performed by photolithography using mercury lamps, KrF excimer lasers, ArF excimer lasers, or the like, as sources of exposure light. In addition, resolution is increased by employing immersion lithography. Further, the use of extreme ultraviolet light having a shorter wavelength as exposure light is also studied.
In this manner, various techniques are studied for pattern miniaturization. Among these techniques, a technique for obtaining a finer pattern by trimming an already formed resist pattern through etching has been recently proposed.
A conventional pattern forming method for obtaining a fine pattern with a trimming technique through etching will be described with reference to FIGS. 9A-9D, 10A, and 10B.
First, a chemically amplified positive resist material having the following composition is prepared.
Base polymer: poly(2-methyl-2-adamanthyl methacrylate (50 mol %)—γ-butyrolactone methacrylate (40 mol %)—2-hydroxy adamantane methacrylate (10 mol %)) . . . 2 g
Photoacid generator: triphenylsulfonium trifluoromethanesulfonic acid . . . 0.05 g
Quencher: triethanolamine . . . 0.002 g
Solvent: propylene glycol monomethyl ether acetate . . . 20 g
Next, as shown in FIG. 9A, the chemically amplified resist material is applied on a substrate 1, and then is heated at a temperature of 90° C. for 60 seconds, thereby forming a resist film 2 with a thickness of 120 nm.
Then, as shown in FIG. 9B, the resist film 2 is irradiated with exposure light which is ArF excimer laser light having a numerical aperture (NA) of 0.93 through a mask 3, thereby performing pattern exposure.
After the pattern exposure, as shown in FIG. 9C, the resist film 2 is heated with a hot plate at a temperature of 110° C. for 60 seconds.
Thereafter, as shown in FIG. 9D, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer, thereby obtaining a first resist pattern 2a made of an unexposed portion of the resist film 2 and having a line width of 60 nm.
Subsequently, as shown in FIG. 10A, the first resist pattern 2a is ashed with an oxygen-based etching gas. Consequently, as shown in FIG. 10B, upper portions and side portions of the first resist pattern 2a are trimmed, thereby obtaining a second resist pattern 2b having a reduced (shrunk) line width of 50 nm.